Enamel coated welded joint



y 1945- w. G. MARTIN 2,374,763

ENAMEL COATED WELDED JOINT Filed Oct. 10, 1942 FIE-3.].

INVENTQR AT TORNEY.

Patented May 1, 1945 ENAMEL COATED WELDED JOINT Wesley G.

Martin, Milwaukee, Wis., asslgnor to A. 0. Smith Corporation, Milwaukee, Win, a corporation of New York Application October 10, 1942, Serial No. 461,581

9 Claims.

This invention relates to enamel coated welded Joints and is applicable in the construction of enamel lined pipe and of connections welded to enamel lined tanks.

In the commercial construction of ceramic lined domestic water heater tanks, for instance,

. it has been the practice to employ an alloy con- Fig. 3 is a similar section through another type of connection for a tank; and

is to prevent crazing of the enamel at the weld juncture between two members of difierent metallic composition.

In accomplishing this object, a discovery of substantial importance and commercial application was made. It was found that. the crazing' of the enamel was primarily caused by the different rates of expansion of the two members underthermal changes, and that if at the line of the joint exposed to the enamel, one member could be made thin and to overlap the thicker and stronger member for a substantial distance,

by that of thestronger member for some distance from the line of joinder, so that the gradient between the movement of one metal mem-' bar and that of the other would not be restricted to the fairhr sharp line of weld or braze,

ceramic or vitreous type bonded to the metal by fusion. v

The accompanying .drawing illustrates typical embodiments of the invention.

Figure 1 of the drawing is a side elevation of two pipes Joined together according to the present invention, with the joint sectioned on its longitudinal center line;

Fig. 2 is a central longitudinal-section through a pipe connection for an enamel lined tank;

' the inside allows it to By reason of this construction the metal of mem- I her 5 immediately adjacent the joinder on the inits movement under its expansion or movement would be controlled Fig. dis a similar section of another type of connection.

Referring to Fig. 1,-the pipe 5 is of ordinary steel while the pipe 2 is of chromium alloy steel. The ends of the two pipes are beveled in a complementary manner so that when abutted together the tapered face of member I fits, into the tapered face of member 2. The two are either resistance welded or brazed together along the frusto-conicalmeeting surfaces 3 therebetween. The members and Z are subsequently lined with vitreous enameling material and the latter is fused to provide an impervious protective lining l bonded to the steel.

The thinning of the edge of the member I on overlap a thicker portion of the edge of member 2 at and for a' substantial distance adjacent to the inside line of joinder.

side will becontrolled in thermal changes by the stronger section of a1- loy steel. The expansion gradient at the joint will be spread over a greater longitudinal distance and the stresses developed will not be sufficiently concentrated to In Fig. 2 the invention has been appliedin attaching a brass nipple 5 to the steel wall 6 ofa tank. Here the metal of the tank wall is flanged outwardly around the opening I and the flange 8 and nipple ii are tapered similar to the tapering of the members in Fig. l. v

The tapered face of nipple 5 fits inside of the tapered face of to along the frusto-conical line 9. Ceramic enam'el it is bonded to the inside of wall 6 and extends over the brazed joint 9.

The thin edge of the brass nipple 5 overlapping the thicker and stronger steel section of the joint results in a control of the movement of the .brass in this region more nearly like the movement of the steel under thermal changes. This prevents undue results in iniury to the enamel.

In Fig. 3 the pipe connection ll, of brass, extends through an opening-in the tank wall 12. The inner end of connection. II has a flange l-3 overlappin the inner the meeting surfaces along the lines of a.frustrum of a cone, as shown, and brazing or welding the two together. The joint ll, thereby provided, has a relatively thin edge of brass, of flange injure the enamel. v

flange 8 and is brazed therestress concentration that surface of the tank wall.- This overlap is preferably obtained by tapering l3, overlying a relatively thick section of the steel tank wall. The enamel lining 15 for the tank extends over the joint and for a short distance over the brass of the connection.

In Fig. 4 the nipple i6 is of ordinary steel butt welded to a flange ll of the tank wall. The

,nipple It has a corrosion resistant alloy lining l8 which is brazed or otherwise secured in the nipple and threaded internally to receive a pipe connection. The lining I 8 is tapered or feathered on its inner end to provide the thin section thereof which is controlled in itsthermal expansion by the thicker and stronger base metal beneath so that the inside line of joinder does'not have concentrated stress that might injure the enamel. The enamel l9 extends as a lining over the butt weld and also' over the brazed liner joint.

In carrying out the invention, there may be advantages in some instances in having the member, constructed of the stronger metal, thinned n the enameled side. On the other hand, in most instances, as in Figs. 2 to 4, inclusive, the

' weaker metal is feathered at the joint on the inside. This makes more certain the gradual control of expansion and contraction so as to prevent concentration of shear stresses in the enamel.

The invention has various applications and embodiments within the scope of the atcompanying claims.

I claim:

1. An article having an integral joint between metallic members of difl'erent composition and coeflicient of expansion and having an enamel coating on one surface thereof extending over the line of the joint and bonded to the surfaces of the respective members, in which one of the members has its edge beveled beneath the enamel coating with the thin edge portion overlapping the relatively thicker section of theother memher and integrally joined thereto.

2. An article aving an integral joint between metallic mem rs of different composition, strength and coefllcient of expansion and having an enamel coating on one surface thereof ex- .tending over the line of the joint, in which the members have their joined faces beveled to provid a substantially thin edge of the weaker memberoverlapping a thicker section of the stronger" member adjacent the line of joinderv immediately beneath the coating.

3. An article having an integral joint between metallic members of different composition, strength and coeflicient of expansion and having an enamel coating on one surface thereof extending over the line of the joint, in which the members have their Joined faces beveled to provide a substantially thin edge of the stronger member overlapping a thicker section of the weaker member adjacent the line of mediately beneath the coating.

Joinder im- 4. An article having an integral butt joint between two metallic members of substantially equal .cross section with different coeflicients of thermal expansion andhaving amfenamel coating enamel coating on one surface bonded to one surface thereof and extending over the line of the joint, in which the members have their edge faces beveled to provide a substan-. tially thin edge of each overlapping a thicker section of the other and secured thereto to efl'ect a more gradual change in rate of thermal expension at the surface from one member to the other across the joint.

5. A tubular article having an integral butt joint between two metallic members of substantially equal cross section with different coemcients of thermal expansion and having a ceramic enamel lining bonded thereto on the inside and extending over the line of the joint, in which the members have their meeting edges beveled to meet in a frustrum of a cone with the thin edge of the member with the lowercoeflicient of expansion fitting inside of the other mem her and controlled in its expansion by said other member to prevent a sharp line of differential movement at the joint tending to injure the bond of the enamel.

6. A tubular article having an integral butt joint between two metallic members of substantially equal cross section with different coefllcients of thermal expansion and having a ceramic enamel lining bonded thereto on the inside and extending over the line of the joint, in which the members have their meeting edges beveled to meet in a frustrum of a cone with the thin edge of the member with e greater coeiiicient of expansion fitting inside of the other member and controlled in its expansion by said other member to prevent a sharp line of differential movement at the joint tending to injure the bond enamel lining 'of the tank extending-over the .brazed joint and being bonded the thin portion thereof.

8. A connection for a ceramic enamel lined steel tank comprising a tubular member butt welded to a flange in the wall of the tank and having a to the fitting over therein with a feathered inner edge over whichthe enamel lining of the tank extends and to which said fining is bonded.

9. An article having an integral joint between metallic members of different composition and coeflici'ents of expansion and having a ceramic thereof extending over theline of the joint, in'which one of the members has a feather edge beneath the enamel coating overlapping the relatively thicker section of the other member and integrally joined thereto to provide a more gradual transition from the coeflicient ofjexpanslon of one member to-that of the other at the surface directly beneath the enamel coating. r

' WESLEYG. MAR'I'IN.

threaded liner at its outer end secured 

